This invention relates to automated vision systems and, more particularly, to methods and apparatus for inspection and placement of surface mounted devices (SMD's).
In automated assembly processes, for example, those for assembling electronic circuit boards, it is important to determine the exact position of components prior to their being positioned for final assembly. Thus, for example, an assembly system must know the axial position and angular orientation of an integrated circuit "chip" before placing its leads on the appropriate pads on the printed circuit board.
The design and size of components that must be placed by these circuit board assembly processes can very greatly. The number and relative size of specific features that must be inspected on those components also vary greatly. It is quite common for a feature to be two to three orders of magnitude smaller than the component as a whole.
Of today's commercially significant components, the smallest measure 1.0 mm by 0.5 mm and consist of a single feature, their rectangular shape. The largest, on the other hand, measure over 50 mm in width and include several hundred features, typically, component leads which, themselves, measure less than 0.25 mm in width.
The outlines of electronic circuit components, or so-called surface mounted devices, are generally polygonal with right angle vertices. They generally have opaque non-conductive bodies of plastic or ceramic from which electrical contacts emanate. These electrical contacts may be leads (rectangular metal strips, possibly bent at one or more points) or pads (metallic regions bonded directly to the body).
Upon initial inspection, these leads and pads may appear to be part of the component body itself. For example, leads may extend away from the body and, thereby, contribute to the component's outline, or they may wrap around underneath the body. Moreover, leads and pads may be tinned. This tends to round corners, increase apparent size, and produce specular reflections and oxidation problems in frontlight.
An SMD inspection and placement machine typically has a "library" of several hundred different component designs. At each assembly step, the machine must inspect and place a component with one of those designs. New component types are being designed continuously as electronic devices and packaging evolve. International standards and widely disseminated specifications typically don't exist until well after a new component's introduction. They may never exist for specialized or proprietary components.
Thus far, the art has failed to provide systems capable of rapidly inspecting a wide variety of SMD's nor those which can be readily updated to accommodate new designs. Traditional solutions have required redesigned software and the release of an update whenever support for a new component is demanded by an end user. This can take many months.
It is, accordingly, an object of this invention to provide an improved automated vision system and, more particularly, an improved method and apparatus for surface mounted device inspection.
A further object of the invention is to provide a surface mounted device inspection system capable of automatically identifying the position of surface mounted devices of varied size and shape.
A still further object of the invention is to provide a surface mounted device inspection system that can be readily updated to inspect new component designs.
Another object is to provide a surface mounted device inspection system capable of automatically determining the acceptability of a component being inspected, that is, for example, determining whether a component has specific features such as leads.
Still other objects of the invention are evident in the description which follows.